unsafeUnwrapErr method
This method is unsafe, and should only be used in a test environments
takes a Result<T, E> and returns a E when the result is an Err,
otherwise it throws a custom object.
@param config
Implementation
@override
E unsafeUnwrapErr({ErrorConfig? config}) =>
throw createNeverThrowError('Called `_unsafeUnwrapErr` on an Ok', this,
config: config);